Step 1 : Upload the pcb manufacturing files (aka gerber files). Download the zip file attached at the end of this post, go to the instant quote page and upload the zip file as-is. This is the latest PCB revision with the "Uzenet extension" which add the ESP8266+SPI RAM.

Step 2 : When upload is complete you can select the options you want. By default all options are the ones required. You can choose the color you want at no extra cost. Optionally you may choose a different surface finish at an extra cost, which is calculated and shown to you in real time. HASL is lead based but is usually the easiest to solder. So that's the best option for beginners.

Step 3 : Add to cart. Just choose the right shipping for you and you're done. As you can see, if you're a bit patient you can get 5 PCBs for under USD 5$!

After creating an account and submitting your order, you can follow the build process and know when it's complete and shipped. Pretty neat.

Once you receive your PCBs, check out the assembly guide: http://uzebox.org/files/UzeboxAssemblyGuideV1.7.pdf
The Bill of material and schematics are available here.
You can also check this youtube video to help out:
Happy building!
Uze